I would say RSM simply because it's a well known school in Europe. Seeing how Europe functions now, it certainly has a higher ROI given that you would be in a situation to work almost anywhere in the EU if you speak the local language. As for HEC Montreal, it's relatively unknown outside of Quebec, why HEC montreal when there are more famous ones in Ontario? The class profile for HEC wouldn't be as diverse as RSM too.
RSM....you win Europe. HEC Montreal.....you win only Quebec and maybe Canada.
Also if you don't speak French, that part of town where HEC is located will be very foreign and sometimes can be hostile to anglophones.......All programs in HEC are in french except for the MBA, so be prepared to study in a very French environment. As for student life and the students themselves, we can only hope that because they are in a B-school, their outlook on issues are international, especially on language; atypical from the narrow mindedness of PQ separatists.