If I use a diffuser will I be able to use a pressure cooker to can food on my glass top stove?
Glass stove top manufacturers sometimes recommend not using pressure canners because the weight and heat distribution can be too much for them and the glass surface can crack.

A diffuser would probably not help with that problem. The diffuser is not likely to be so much bigger than the canner that it would distribute the weight. If it was that large then it would diffuse the heat too much.

Sometimes stove or canner manuals will place restrictions on the size of the canner vs the burner size. If the canner is too large it can transfer heat out of the burner area and damage the surface.

Another common problem mentioned is that some canners have concave bottoms. Obviously, only flat bottomed canners should be used otherwise the weight distribution will be bad for the burner and the canner might not heat properly.

You should check with the manufacturer of your range and see if your range can be used with a pressure canner. If they say it can can then you can can without the diffuser. If they say it can't then you may just be out of luck.

We use a camp stove and do a lot of our pressure canning outside- especially in the summer to save AC bills.

Anecdotally- My mother once, 20 years ago, had a glass surface crack while canning. I have been canning on a glass surface for two years without incident.