Submitting Amended T4 Summary and T4's

Can I EFILE amended T4 Summary and Amended T4’s or do I have to send via mail?

You can amend it in TaxCycle. Just check the box that now likely says “original” and choose “amended”. Then you can transmit the amended slip(s) the same way that you transmitted the original slip(s).

Awesome. Thank you so much for your help, Kevin.