Update: received this message this morning from Canvas Support which confirms reason why initial upload is lower resolution. Give it some time...took 6 hours for my uploaded videos to appear at high resolution yesterday!
"Thanks for contacting Canvas Support. I understand that you encountered some behavior within Studio where videos that you uploaded had a significantly lower resolution or quality than you were used to.
When the videos are first uploaded they are placed into a queue of videos to be processed. The initial processing of the video when uploading allows for the video to simply be viewed within Canvas/Studio and as time goes on they should see an increase in quality. In addition to this I do see that your uploaded videos in your course that came linked to this ticket are currently playing for me at the highest quality. These videos do also show a gear icon in the lower right corner of the video player and viewers can select this gear icon to choose video quality.
Have a great day,
L1 Canvas Support"