There are over 2000 window manufacturers in Canada, and with all that competition, each one wants to make homeowners, renovators, and builders believe that their windows are easier to install than the other brand. This has led to a lot of very poorly built windows that are often difficult to install well. For instance, many windows now come with a nailing flange, and the literature will often say that all you have to do is prop the window up and screw the nailing flange to the wall and it is installed. The reality is that this window will not perform well over time. Nor will one that is attached by its brick molding. All the weight is on one side of the nailing flange, eventually twisting the whole thing out of shape and breaking water-proof seals.
One of the important details in all of this is that the bottom and the sides of the window must be properly shimmed, with full support by shims placed in the right places. This does not mean that the inside is holding up the window, or that the outside nailing flange is holding up the window, but that the shims are placed in pairs so that their upper and lower surfaces are parallel, and they are placed and spaced properly. No shims at the top, to allow for movement from weight above. Shims on the sides near hinge positions. Shims across the bottom. But no shims directly at the corners of the window, to allow for some expansion and contraction of the vertical and horizontal frame of the window. Screws either go into the shims, or right alongside the shims, but not too far from the shims where they would tend to bend the frame. All of these details apply to all types of windows: wood, vinyl, aluminum and fiberglass.