Hi Pascal:
Not sure if you're still monitoring responses as I've only come across this thread now.  But my suggestion would be:
Yes a pop up shop would be great.
Do your homework and come visit Toronto and surrounding areas.  You'll get a great "feel" for how people  and eat here. [as a former Montrealer, I can attest to that]   For example, I live near the St. Clair St area near one of the best Loblaws - another will be built just up the street.  The one on St. Clair West has a huge aged beef cooler right near their butcher department.  The meat is beautiful.  So even in a grocery store, you can get the highest quality meat in the country.
Ultimately, you may want to invest one day in a store here - that way people could say they were shopping "locally" which is a big deal these days.  
Last suggestion:  what would you tell an Ontario butcher who wanted to break into the Quebec market to do?  Not so easy, right?  But there are ways.
Bon chance!  I hope you do well.