They have the range to make it to Europe from YOW. And otherwise, yeah, they are already here sometimes on YYZ/YOW routes (they ferry the 767s to YYZ too, crew are not based in YOW already).

I can see 888/889 going to 7M8 year round and 838/839 operating in the summer on a 788, maybe 5 days a week. Want a J seat to LHR? Connect in YYZ or YUL. Not like there is another option...