Yes, but also no. It's a bit deeper then just the monarchy.

This sentiment is coming from two political parties/sources: the federal Bloc Quebeqois, and the provincial Parti Quebecois. Both of them are Quebec Separatist parties that want an independent Quebec.

The issue is they don't want to swear allegiance to the head of state of Canada, who now happens to be King Charles. It isn't really so much an anti-monarchy statement so much as it an anti-confederation statement, coming from them.

The brexit joke is that Canada dropping the monarchy would open a massive unknown can of worms similar to what Brexit did, while actual Quebec separation would be a boondoggle for them that would make Brexit look like a picnic.