I'm a newbie here too. Seems to me that the solution might be to select flat rate & disable auctivia's checkout. Then manually "revise" your listing on eBay.ca directly. I'm not sure if this will work... I'm gonna try it tomorrow. You'd likely have to disable auto re list as well.
I guess the only thing auctivia has for us Canadians is the templates. Time to learn html.