Thank you for mentioning that the OSM-ca Slack invite isn't working, I'm not sure who was the maintainer of the invite app so I added new invite links to the wiki pages instead. (Personally I am really not a fan of how Slack workspaces need an 'invite' link to join and there's no option of a permanent invite link, but some other people were there...) The Slack isn't very active so you might not be missing much. I believe you are also aware of the new Canadian community on the OSM Community Forum <https://community.openstreetmap.org/c/communities/ca/95> which might be an easier place to discuss changing the guidelines.

To be honest, I continue to be confused about why you are asking about Manitoba in particular. There are plenty of regions in OSM where roads are classified based on their legal classification rather than network significance. As you might be aware OSM road classification started out with "primary" being drawn directly from UK's primary roads which have A numbers.

I mentioned Unst above, it is an island of 600 people with a highway=primary. Will you be asking UK editors to change the OSM classification of its A road? There's highway=trunk on Lofoten archipelago on northern Norway all the way to a dead end in a town with a population of less than a thousand, should E10 be reclassified there?