Don't go cheap.
I bought some canvas that was not expensive but looked a perfect match. However the colour quickly bleached out .
I find the best method is to take the canvas to the workshop that made it . They are happy to carry out repairs eg new windows and a new zip last year . Not for free of course but a lot cheaper than a new canopy.
Have used Sauleda for sprayhood, bimini, dodgers and sail cover. Last Sauleda sprayhood lasted about 18 years and bimini a bit less, in high UV area. Colour didn't fade much.
If this looks like the right colour, and you only need a repair patch, PM me and i can post you a piece from Northern Ireland EDIT - having difficulty uploading image!
Sunbrella .... as I found out not exactly as strong as it looks ....
Watch closely guy at sprayhood ... when we hit that sprayhood - BRAND SPANKING NEW ... it tore so easily ...
It was why boat was away from home mooring - having new hood ... dodgers .... sail covers made along with new rubbing strakes.
The old hood even after 25 odd yrs .. would most likely have survived that ... but it was getting tatty .. windows were shot and overall condition was showing real age.
I took hood back to the yard who made it and asked them to double up in areas to strengthen ... its a 25ft boat that goes to sea ... if the hood cannot stand a person falling on it - it has no place on the boat ...
I have read online reports of Sunbrella not being best material .... seems I found out.