I am replying to your question because, although I don't have specific knowledge of SFCR I appreciate your frustration when trying to convince senior management team of the necessity of something, especially where it might require some human or financial resource.
I'm assuming you're not BRC accredited - a shame as BRC V8 has implemented a specific new element (9.0) to manage approval & performance of manufacturers of traded food products?. I believe SFCR has a key requirement for preventative control plan (PCP) which involves knowing the product & knowing the supplier?...
Without full approval of your suppliers it would be difficult to write this PCP?...although your products may be sealed on arrival, if you don't have confidence in your supplier (supplier approval) you don't know what sort of risks there may be at their manufacturing site? and I agree with your position because preventing an issue is quicker/safer/cheaper than responding to an incident.
UK legislation is very clear on this - the importer has the responsibility of ensuring that the supplier is complying with all relevant legislation in the country of sale (UK) & is subject to prosecution if there is a food safety incident.
I believe Canada has similar regulations (CCPSA) and consequences can be quite severe, so a quick search on the net of historic recalls of imported foodstuffs (and the consequences) is usually sufficient to "focus" the minds of the team on the level of risk & hopefully convince those concerned of the need to do this!.
It shouldn't take long to set this up, even approval via 3rd party GFSI audit status (?) or completion of a detailed supplier assurance questionnaire (SAQ) would provide a good starting point?...
Best of luck!!