Substituting canned tomatoes for fresh?

Sounds like a great dish! Just another thought about using the canned tomatoes - which I agree will be fine - and their liquid.
The liquid may be more than the fresh tomatoes give off, so I'd drain it and add the canned tomatoes alone to the dish. Add tomato liquid as needed, at the beginning of roasting and/or when you check it near the end.
If you have leftover tomato water, save if for smoothies or soup.

I think you could use canned whole tomatoes. The time needed for the tomatoes to soften deceases, but you want to be sure that you roast long enough for the herbs, other liquids and seasonings to permeate the tomatoes.