At first I thought that the breather tube on eBay would not work on the 77 Can Am, since that tube is for 73-76 Pontiacs. I know 77 and up Trans Ams use a different tube that is shorter and straighter than the earlier, longer, curvier one. The reason for the difference was because the 76 and earlier air cleaners had the hole further forward on the air cleaner base, so the tube has to be longer to reach it. In 77, they moved the hole to the side of the air cleaner for a straighter shot to the valve cover.
But, after looking at photos of several Can Ams, I can see that the 77 Can Am actually still uses the older, 73-76 style breather tube.
So, moontower69 was correct in referring you to the 73-76 tube on eBay.
Here's a new reproduction, but it says for 68-74. It looks the same, so I don't know why it wouldn't work.
https://www.ebay.com/itm/68-74-Ponti...vjU:rk:20:pf:0