I am obtaining the printer's IP address on my Network (either by printing out the Network Information page on my printer, or by inspecting the "Attached Devices" page on my Netgear router. I am then using a web browser to access the printer's Remote Interface, using the local IP address I have determined. I click on Google Cloud Print setup; on the next page I click on Register with Google Cloud Print; on the next page I click on the Yes button; on the next page English is already selected as my chosen language, and I click on the Authentication button. A blank web page opens in another tab on my browser and after a considerable wait it closes again and I get a Registration failed message on the Authentication page. It would appear that the printer is having problems communicating with Google?
I am following the steps as indicated. (It is interesting that you have obtained a Canon "kb" article that gives the correct method of printing off a network information page, as the on-line manual for the printer gives incorrect information, and the only source I had found of the correct information was a Youtube video.)
I am using Chrome on my iMac to access the RUI of the printer. I have also tried Safari. My wife has a Windows 8 laptop, so I could try using IE (I would have to be really desperate to go down the Microsoft route!)
Exactly the same result with Internet Explorer
The Youtube video you referenced relates to Pixma printers with a built-in display. The MG3500 series do not have a built-in display. Printer settings and registration with Google Cloud Print are effected via a web browser running on a device on the same LAN. For this reason it is impossible for me to follow the steps in the video.
It seems the professional has left this conversation. This happens occasionally, and it's usually because the professional thinks that someone else might be a better match for your question. I've been working hard to find a new professional to assist you with your question, but sometimes finding the right professional can take a little longer than expected.
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Thanks for your patience,