Do I need a minor variance if my planned garden suite doesn't meet the standard setback rules?

Yes, generally. If your garden suite is otherwise a permitted use under your municipality's current bylaw but the specific proposed location doesn't meet a standard requirement like a setback from the property line, that's exactly the kind of situation a minor variance is designed for: seeking limited relief from a specific numeric requirement while the underlying use itself remains permitted.

The committee of adjustment would evaluate the requested setback reduction against the established four-part test, considering whether the reduced setback is minor in the context of your property and neighbours, whether it's desirable for the appropriate development of the land, and whether it still respects the general intent of the zoning bylaw and official plan. Practical factors like how the reduced setback affects a neighbour's privacy, drainage, or line of sight often come up at the hearing, so it helps to address those specifically in your application materials rather than focusing only on the numeric gap. If the setback issue is significant enough that the committee, or your own planning advisor, doesn't think it qualifies as minor, redesigning the suite to meet the standard setback may ultimately be simpler than pursuing a contested variance.