The dramatic thing about this story is that it starts with an oath. Abraham causes Eliezer to swear that he will not bring a Canaanite bride to Isaac.
Why was such an oath necessary? Eliezer was Abraham's servant. Servants are supposed to follow orders without having to swear about everything. Secondly, why does Abraham not cause him to swear that he will bring back a wife from Abraham's family in Mesopotamia? The emphasis of the oath is on Eliezer NOT bringing back a Canaanite girl! Why the negative?
Finally, fundamentally, why was Abraham so opposed to a Canaanite girl? Eliezer himself had a daughter who was of the right age. It stands to reason that she was a very good girl, considering who her father was an in what house she had grown up. The reason given by the rabbis is that the Canaanites are the descendents of Ham, who was cursed by Noah. Abraham is the descendent of Shem, who was blessed by Noah. "Blessed should not cleave to cursed."
The Or Hachaim puts words to this argument. After all, he reasons, Abraham was blessed. He was given the ability to confer that blessing upon others, and all that are in his family are recipients of blessing. Shouldn't all of this blessing be enough to negate the curse of Noah?
Furthermore, Abraham's family in Mesopotamia are no great shakes. We are talking about idolaters and cheaters. In fact, according to the midrash, Rebecca's father Betuel dies by ingesting poison that he had intended for Eliezer! Rebecca's brother, Laban, is a legendary manipulator who harbors ill intentions towards Jacob and his family. Are these people really a better source for a wife for Isaac than the family of Eliezer, faithful servant of Abraham?
The answers to these two questions are foundational for every matchmaker. The first question, why was Eliezer tasked and not Isaac himself, can be answered by a clichéd but true fact: no two people are created alike. Every single is their own unique personality. Isaac, as can be seen throughout his life, is a passive person. He is a great Tsaddik, but he does not innovate or initiate. Therefore, Abraham does not trust him to find his own partner.
In relationships, there are different dynamics. Some seek a parental figure, while others look for someone whom they can nurture. Still others are looking for a sibling or a friend or a playmate. There are many nuances in relationship seeking, but these are the main categories. Isaac, as a more passive person, would naturally gravitate towards a motherly figure. This is born out by the Torah, which reports that "Isaac brought her into his tent, he loved her, and was comforted after his mother."
As a side note, we should note that Isaac loved Rebecca only after he brought her into his tent. Love, in this verse, is a verb. It is not something that one "falls into." It is, instead, something one must do to succeed. Attraction is like the sign outside of a restaurant. It'll get you in, but what you order on the menu will either leave you happy or sick to your stomach. The success of a matches dependent on what happens after the canopy, not before.
This understanding of the importance of each individual's psychological and emotional makeup points us to the answer to the second series of questions. In short, ideology can be changed fairly easily. Character, however, cannot.
The Canaanites were cursed because of the character of their grandfather, Ham. His was a character of selfishness, lack of responsibility and lack of concern for others. A normal child, upon seeing his father in a degraded state, would rush to restore his father's dignity. Ham, on the other hand, not only failed to do so, but (according to a midrash) sterilized his father! To be capable of such an action one must have a deep corruption in one's basic character. That is the source of the curse, and that is the character trait that exhibited itself in Ham's descendents who dwelled in Sodom and Gomorrah.
So while it is possible that a Canaanite can be an exemplary citizen, there is no guarantee that good character will survive to the next generation. And, considering that Isaac is a more passive person who needs a mother figure, it could be Isaac who becomes corrupted rather than the bride who becomes inspired.
So Abraham understood that ideology can be changed easily. The idolatry of his family did not concern him, since he knew that kindness was deep-rooted. Even though Betuel and Laban were no great paragons of virtue, they were the exceptions in the family. What's more, it is eminently possible that their opposition to the family of Abraham is born of their fear of Abraham's monotheistic faith threatening their comfortable idolatrous lifestyle. They weren't bad people, but they did bad things out of a sense of panic.
And, at the end of the day, they enable the match of Isaac and Rebecca as well as the future matches of Jacob, Rachel and Leah.
The medrash tells us that when Isaac brought Rebecca home, four things happened. Four things that had been present when Sara was alive and disappeared with her death, returned with the entrance of Rebecca. There was a cloud on the tent, there was a blessing in the dough, the doors were always wide open, and a candle was lit from the eve of the Sabbath to the next eve of the Sabbath. What do these four things mean?
The cloud symbolizes the Divine Presence. This rested upon the tent as long as three crucial things were in place. My teacher, Rabbi Ahron Soloveichik, explains these three things. 1. The home had to be one of mercy. The Sabbath is a day of peace, a day of living together in harmony. When the Torah prohibits fire on the Sabbath day, the Rabbi's comment that this includes the fires of fighting an argument. This is what it means by the candle being lit from Sabbath to Sabbath, meaning that the spirit of peace of the Sabbath pervades the entire week. This comes from the character trait of mercy. 2. The home has to be one of modesty. The sages tell us that the one who is truly wealthy is the one who is happy with his lot. This is what it means by a blessing being in the dough. The family feels blessed with whatever it is they have. This is the character trait of modesty. 3. The home has to be one where kindness is prevalent. The sages tell us that we are to always have our houses open for the relief of those who are in need. This is what it means by the doors being open all the time. This comes from the character trait of kindness.
These character traits are the opposite of the heritage of Ham, Canaan, and the Sodomites. Abraham teaches every matchmaker that interests and ideology may be an external factor in a match, but the true energy lies in compatible character traits. "The way of the world (good character) comes before Torah," say our sages.