I planted a cherry tree in a sunny spot last May. This year I saw budding on all the branches, but only one branch grew leaves. The rest of the buds just dried off. I dont know what is wrong with the tree.
It appears that your young tree has suffered severe winter dieback. Winter dieback is caused when harsh winter conditions kill the cells in buds and branches. Trees need leaves to survive, so if most of the leaves have not emerged this year, it is likely your tree will not survive. Many nurseries have a guarantee on new trees, so you may want to contact the nursery where you purchased the tree to see if they will replace it.
If you decide to replace the tree, make sure you select a variety that is sufficiently hardy for your area. You can determine your hardiness zone here. The Ontario Ministry of Agriculture, Food and Rural Affairs has a list common cherry tree varieties that grow well in Ontario and their specific hardiness zones.
It is important that newly planted young trees have the optimal conditions to ensure they thrive, particularly as they go into their first winter in their new location. If you decide to replace the tree, you may want to reference the Toronto Master Gardeners Guide on tree planting to ensure you are giving your new tree the best possible start.