I live in Ontario Canada we are having temperate of -10 now
I have put my young potted bonsai in my unseated garage until spring
Should I water all winter ?

In winter you water the same way as in summer......When the tree needs it, not on a scedule. Naturally the trees use less and transpiration is less hence much less frequent. In my climate similar to usda zone 7, I water 1-3 times on my protected trees. The trees outdoors rarelly get any watering october to march, rain is enough here.

With this sort of weather it is important to water when the plant thaws out. When forzen, watering is of little use.

In the garage it will not be exposed to wind or sun, so the above-ground areas do not run as much risk of dessication as those standing outside.: Keep in mind, frozen roots cannot take up water. So a plant in apot in the sun can dry out when the roots are frozen.