What actually protects a homeowner is licensing, not union membership: electrical, gas and plumbing work all require a licensed tradesperson and a permit before the City of Saskatoon will sign off, and that requirement applies equally on a union and a non-union job site, the same standard a $400 to $600 home inspection checks for later.
Larger commercial and institutional projects in Saskatchewan sometimes carry union agreements for wage and training reasons, but that is a separate labour relations question from residential building safety, and it does not change what a single-family home renovation needs to pass inspection.
For a homeowner, the safety question that actually matters is whether the permits and inspections happened, not who employed the crew. Get your hand-reviewed valuation from Joel Dyck.