No, I don't think it's that difficult. I actually think you could put a strong DC tie-line between Quebec and Ontario, a strong DC tie-line between, perhaps, Manitoba and Saskatchewan, and more AC tie-lines between Alberta and B.C., because somebody has already discussed the potential to help each other between B.C. and Alberta. Certainly, there is a lot that could be done there.
Where you are risking connection of two very big systems.... I teach electric power systems, and I compare this to two elephants running down the road, tied together by a thin piece of thread. It doesn't take much of a divergence to break it.
The advantage of DC is that it would allow you to shift power back and forth without a big problem. If you look at Europe, England is connected to Europe all with DC lines, and that's exactly why.