Only the combination of two conditions would cause the wax to rub off of a waxed canvas bag and transfer to another material (like car upholstery or a pant leg): application of excessive wax + extremely warm temperatures.
Waxed canvas bags from a manufacturer (not DIY projects) are not typically made by rubbing oil or wax onto the canvas, but rather the canvas is produced with the wax or oil embedded into the canvas fibers. This means, even in hotter climates, you shouldn’t experience problems with the wax rubbing off or transferring. Although, for the integrity of your bag, it’s still recommended that you not leave it sitting in something like a hot car for extended periods of time.
If you’ve waxed or re-waxed your own bag and notice some wax rubbing off or transferring to other materials, it’s likely you have applied too much wax to the canvas. Warm the fabric with a blow dryer and repeat the step of working the wax into the canvas. Notice if wax remains on the surface, rather than working into the fabric, and wipe off the excess. Allow to dry and cure again for 24-48 hours.
Overall, remember waxed canvas changes appearance over time. It will show scuffs and marks, and it will become shiny in places. Don’t worry about that stuff - it’s what makes waxed canvas unique and, in most cases, is not evidence of the wax “rubbing off.”