Also depends on which Godzilla you match ( Godzilla from the 60 & 70 ) v.s Gamera of 90 trilogy yes but Godzilla from the 90 / Millenium /Final Wars ...NO WAY
It depends, if you go by the Gamera from the old films he'll lose but put up a fight, if you go by the 90s trilogy then he might be able to beat Godzilla but if you go by Gamera the brave............dear lord Godzilla will wipe the floor with Toto Gamera.
If we're going on durability displayed in the movies, Godzilla hands down. If it ever became a movie, though, I can imagine they would scale them both size- and powers-wise. Cool pic.
Hard to say, Gamera's shell would most-likely withstand even the spiral ray, Godzilla's skin would mostly be immune to Gamera's fire and his regen-factor would have him get over the mana blast quickly, plus as already said, they would be feeding eachother, plus Gamera's onlt soft spot is his underside which Godzilla would realize and a physical fight wouldn't mean anything because they are both pretty tough.
Considering it's a Godzilla film, they will fight until Destroyah or Gigan or whoever else attacks and Godzilla and Gamera work together, defeat bad guy, become friends, exchange phone numbers, and part ways.