I am new to Obsidian and there fore also to the canvas plugin.
I use Obsidian on both iPad and Mac and therefore use sync over iCloud.
With normal Notes links between notes works across Obsidian for iOS and Mac, but when using the Canvas link to Notes break when created i one client and showed in the other.
On your iPad: open the Files app, go to iCloud Drive/Obsidian/YOUR-VAULT/, and check that the DnA... folder and its contents are there, no clouds with arrows, and not greyed out or anything. I’d check there first just to be sure the files are on your iPad.