The indirect channel runs through bond yields. When Fed uncertainty pushes US bond yields around, Canadian bond yields often move with them to some degree, and fixed mortgage rates here are priced off Canadian bond yields plus a lender's own margin, which is how a US policy disagreement can nudge a Saskatoon rate without the Bank of Canada moving its own rate at all.
Variable rates are more insulated from that channel, since they track the Bank of Canada's own rate decisions directly rather than bond market sentiment, which is one reason the same news event can move fixed and variable rate offers by different amounts even for a borrower who clears CMHC's minimum credit score of 600.
A mortgage broker watching both central banks can translate what a specific week's news means for your actual rate offer. Get your hand-reviewed valuation from Joel Dyck.