Providing abortion services for Americans does not cost us as they would have to pay.
However, IMHO OP's plan is silly and misguided. Most boarding states allow for abortion, and those that don't are closer to states that allow for abortion. The vast majority of states that restrict abortion are in the south, and the population who live under abortion restrictions are even more skewed south. This means even if people needing abortions wanted to come to Canada, they'd be more likely to enter at airports instead of land boarders.