Hi
@Rick and welcome to the forum.
A lot depends on the type of canvas but we had a mould issue with a canvas tent we had years ago and the following seemed to work (It did leave a slight stain but at least we got rid of the mould).
The first step is to let the canvas dry out in the sun to kill the mould & then brush the affected areas with a stiff brush.
When dry try a solution of soap and water... Let it soak in until nearly dry and wipe off with a wet rag or sponge.
If the soap doesn't work then try 50 mm of vinegar (White from memory) in 1 litre of water and spray on the mould. Let it soak in for 5 - 10 minutes and wipe or rinse off with fresh water. Would recommend to try a small area out of sight first!!!!!
Unfortunately any cleaning or scrubbing may remove the waterproofing (What???? I hear some ask..... The canvas is waterproof?

) so you may need to re-seal/re-waterproof the canvas. Probably pay to call a Jayco dealer to find out the best waterproofing agent to use.