I'm with Marbles on this one. Accepting all cultures is important, even if there are cultures we disagree with. This does not mean we need to change our laws to be flexibity to other cultures, but it does mean that we accept all of them. If we don't, then as Marbles said, we're hypocrites for calling ourself a free society. A free society, accepts all peoples of all walks of ideologies, but they still have to abide by our socially-contracted rules.
I know RWA is hinting on Sharia law and this is where my second point comes in. Currently Muslims are abiding by our laws by introducing Sharia based civil arbitration in Ontario. However, if that law is deemed un-constitutional (read: against the Canadian Charter of Freedoms and Rights), than it will be tossed.
In addition, if our culture as Canadians is so lax that we all multi-broad based legal systems to be implemented and stayed, then our society will either have to adjust because it is not strong enough or redefine what it means to be a Canadian. Personally, I believe that Canadian culture and society will not accept that.