I haven't had much Avid time lately, so my best suggestion would be MPEG Stream Clip. If you'd doing SD, I'd suggest transcoding your Go Pro video to the same format you're editing in (or as close as possible.)
(MPEG Streamclip is such a good free media converter, that I once even had someone from Apple tech support tell me to use it since FCS didn't have any method of bringing in video off a DVD.)
As far as I know the GoPro only shoots 16:9 so if you're working in a 4:3 project you're going to have to resize it.
When it shoots in 720x960 it is 4:3. Everything else is 16:9
* 960p = 1280×960 pixels (4:3), 30 fps, 12 Mbit/s data rate
* 720p = 1280×720 pixels (16:9), 30 fps, 8 Mbit/s data rate
* WVGA = 848×480 pixels (16:9), 60 fps, 8 Mbit/s data rate
The HD Hero shoots in additional 2 modes over the 960.
* 1080p = 1920×1080 pixels (16:9), 30 fps, 15 Mbit/s data rate
* 720p = 1280×720 pixels (16:9), 60 fps, 15 Mbit/s data rate
I think when it takes still images it does it in a 4:3 aspect ratio. I did some time lapse with my HD Hero & then brought it into Compressor & used a custom ProRes Codec to make it more FCP friendly. But again, not too helpful if you're using an older Avid system.