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Air Canada was one of the earliest operators of the RJ, and at the time, only mainline carriers operated jets, or at least that was the prevailing mentality (the exception being a handful of BAe 146s). Therefore, since 1995 or so, the RJs have always been flown by Air Canada pilots, so the payscale is quite a bit higher than your typical contemporary regional. You basically had mainline pilots/wages flying regional jets.
However, when AC bought Canadian Airlines in 2000, it also amalgamated both carriers' regionals into one huge entity, Air Canada Jazz. It was around this time that Jazz also recieved their first RJs (from Midway I believe), at payscale closer to what other regionals offer. So for the past few years, RJs flown by mainline pilots were flying side by side with RJs flown by regional pilot. As Air Canada deploys much of their RJ fleet to American destinations, they found having RJs flown by mainline pilots competeing against US regionals flown by regional pilots was not good for business.
So, the plan now is to transfer all the RJs to Jazz. Jazz has also ordered the RJ-705 (the RJ-900 bascially certified for RJ-700 seating) to repace those older BAe 146s. Air Canada however, has ordered the EMB 190/175 for its mainline fleet. So Jazz will fly all the Bombardier jets, AC all the Embraers. I'm not sure if the payscale for the RJ-705 at Jazz is similar to the EMB 190/175 at AC mainline, as they are almost identical in capacity.
Simple, eh?