Start with the trail
Watch long enough to see where ants enter and where they are travelling. Clean the trail after you have learned from it; wiping first can erase the clue.
Food and moisture
Crumbs, pet food, recycling residue, syrup, sink moisture and leaking plumbing can keep activity going. Store food in sealed containers and correct leaks before judging a treatment.
Baits versus contact sprays
A contact spray may kill visible workers without reaching the colony. A registered bait can be useful for some species and situations, but only when the label names the use and placement.
When to escalate
Carpenter-ant activity, repeated emergence from walls, large numbers after repeated sanitation/exclusion, or uncertainty about the species are reasons to get a professional identification.
Canadian rule: if a pesticide is part of the plan, use only a product registered in Canada and follow the label for the named pest and treatment location. Provincial and municipal restrictions can still apply.