Thank you for posting your query and welcome to Rogers Community Forums. 😃
There is no easy way to move all your @rogers.com emails to @iCloud.com. How do you normally check your @rogers.com emails?
If you are trying to backup your @rogers.com emails, then the best option is to use an email client like Microsoft Outlook or the default mail client etc. and download them to your computer. In this way, you can backup both of your email accounts to iCloud.
Let us know if you have further questions.
I assume you're using Apple devices like an iPhone or iPad. An option would be to utilize the "Mail" app which comes free with iDevices. If you set it up for IMAP, then you should be able to "synchronize" Mail with Webmail. This will take some time if you have a lot of e-mails and you may need to click on the various folders within Mail on the device to precipitate the downloads to Mail on your device.
I recently did this on my latest iPad Air 4. Once all your e-mails are synched (and you have checked various e-mails in various folders) you can save to the iCloud, or even to another device like a Mac computer, which is what I do for all my iDevices (saved to a Mac Mini, which is backed up weekly).