Can I use 18" winter tires and rims with a 19" Sport Package?

[Jon SS]

I am in Canada and will probably be ordering the 3.0si soon with Sport package (different to the US, we have sport suspension but no adaptive handling). It will come with 19" all seasons, can I put 18" winter tires (with their own rims) on the SUV? Or should I stick to 19" winter tires. I read somewhere that you should not go above 18" for winter tires, but I also read that you should match the winter tire size to what comes with the vehicle?

Thanks.