Amazon sells 6" wide self adhesive vinyl paint protection film tape from 3M.
Cut two lengths, long enough to cover the flat bit of the gap between the canopy leading edge and the cowl.
On one of them, trim off an inch of width, so you have a strip that's 6" wide and another strip that's 5" wide.
Peel off the backing and stick the sticky sides together, so you have a 6" wide strip with 0.5" of stickiness along each long edge, and a 5" bit in the middle that's not sticky at all. (or trim the whole lot narrower if you want, it's up to you and your personal aesthetic)
Apply it over the gap with the canopy closed, so it sits flat and flush with the fuselage. Leave it for long enough for the glue to go off properly; Then you should be able to open and close your canopy without interference, and when it's closed almost all of the gap will be covered over with waterproof vinyl.
It gets a bit yellow with age, and shows up any dirt that gets underneath it. But it's cheap, and you can replace it whenever you get sick of looking at it.
You can see it in the attached photo. It got replaced a couple of weeks after it was taken 'cos I got sick of looking at it :-)
In concert with a bead of synthetic rubber doorway draft-seal from Home Depot along the entire length of the hinge line, I've found that this almost completely prevents ingress of water, even in moderate rain.
(Not my idea, it came from Lyndon Tretheway at Custom Aircraft Centre in Goolwa, South Australia)