Large video / lecture capture / screen recording files are too big to go to Canvas directly.
Upload to Mediaspace with Kaltura (to embed in your Canvas course): https://kb.wisc.edu/luwmad/page.php?id=42443
If uploading content to Kaltura doesn’t work, try instead Box, Google Drive, or even YouTube. Any of these tools could be more robust to high traffic. Uploading a video to YouTube is super easy: create an account for yourself, preferably using your wisc.edu google account, then click on “create” (near top right). One advantage to using YouTube is that students can choose to stream your video with very low resolution, if their internet access is poor (gear icon on bottom right, or ⋮ menu in the top right on mobile device > quality > 144p, say).