I am not sure you have enough room to do all you want to do in this yard. I see you have furniture for seating AND you want a vegetable garden and fruit trees. A standard apple tree is about 25 feet tall with a crown diameter of about 25 feet. With a yard of 20 x 28, one apple tree will shade nearly the whole thing. Veggies don't grow well in shade.

Dwarf fruit trees only grow 8 - 10 ft tall and wide and seem the obvious choice for your small yard. Semi-dwarf trees get around 15 ft tall and wide. Look for self-fruiting types, because, as littlebug mentioned, you don't have a lot of room. However, fruit trees are best planted as one-year or, at most, two-year old plants, so it will be years before the tree reaches maximum size. Here is a LINK with information on planting fruit trees in Ontario. Check with local nurseries to see which types will do best in your area.

You can in the meantime plant a garden. If drainage is a problem RAISED BEDS are the solution. Regardless, make sure you can reach every part of the beds. Do not make your beds wider than 4 ft and put taller plants where they will not shade out shorter ones. Make sure all wood that touches soil is rot resistant.

The garden area should be thoroughly turned and all grass and weed roots removed. Soil with gravel in it is not usually a problem unless you are growing root vegetables. Most soils have sufficient minerals available that one only needs to add plenty of well-decomposed compost. Here is a LINK to an article on small space vegetable gardening.