No one is stopping them from splitting off and creating their own Christian political party. Canada does not have a 2 party system. If you can't morally agree with the party you're aligned with, then you're in the wrong party.
A quick check on Google also confirms my suspicion that being Christian doesn't mean you have to be anti abortion. http://www.beliefnet.com/News/2003/01/The-Biblical-Basis-Forbeing-Pro-Choice.aspx
Non religious people can be just as morally conflicted. My wife is not religious, firmly anti abortion, and still married to me, pro choice. I guess it's compatible, my belief is that it's her choice. Pro choice is not equal to pro abortion...