There is a large portion of the federal government that have tied up Canadian economic interests in the tar sands. Entire regions of the central provinces are literally propped up on tar sands extraction. Take that away and you'll have swaths of blue-collar workers with mortgages, debts, and families and no income. They will probably be pretty mad.
Any group that harms tar sands extraction operations harms Canadian citizens... I can see the logic there.
The scary thing is the wider implications of C51 and that it hasn't been voted out, just tabled. This sort of thing winds up being buried in another bill with more obscure language around it when everyone has moved on.