While it's not truly combining, some airlines (though I don't know specifically about Delta or Air Canada) allow one-way flight awards. If the airlines you have miles with allow that, but you don't have enough in either for a round trip award, you could then fly one direction on miles with airline A and the other direction on miles with ailrine B.
In general, it is very hard to truly combine miles/points from different programs, with the main exception being if you have hotel program points and want to move them to miles (that's usually easy). There are a few cases where you can move airline miles to hotel points, but they're rare. And there are no cases where you can move airline miles directly from one airline to another (except for the special exception of airline mergers), or from one hotel program to another hotel program.