The Canon XA50 footage is .mp4 (MXF) and the other footage source is an iPhone 13 Pro set for Most Compatible (vs High Efficiency). Any Adobe Premiere users have experience with a setting that works to combine these two types of footage in a sequence?
Rather than focus on the source, I always suggest that one starts with the end in mind.
What and where are you delivering to? Will the file size be HD, 2K, UHD, 4K, or..? Is the main outlet vertical or horizontal? (Example 9:16 or 16:9)
Once you have an idea of distribution, then you might want to look at which one of your cameras are the main source of footage? Where is your audio coming from?
I’ve just recently delivered a mixed format edit from a variety of sources including social media clips, where we choose DNX 1080p for our sequence setting. The first export master was ProRes 4444 for the external grade. The graded file was imported with audio mix to PPro, and then exported out as ProRes HQ for the end-client.
Worked well. But only because the production had a clear set of specifications for delivery.
Keep in mind, that if one codec doesn’t work for you, you can copy the content of that timeline into another timeline. Only thing to watch out for, is how the aspect ratio reacts.