Thanks for the additional information!
I checked about this sleep mode problem and noticed that many people seem to be experiencing it with other Canon multi-functional printers as well. A solution to the problem quite surprised me - you need to change the wireless modem settings to work only on 20 MHz channel, rather than 40 MHz channel or Auto.
Check the discussion between several Canon users here:
It is for model MF8380CDW, but it should work for your model as well.
This sleep problem must have started to occur for you when changing the wireless router, or when you switched from wired to wireless connection. The printer uses different energy saving mode depending on how it is connected to the network.
Based on the printer specifications available on this link:
the printer consumes 23 Watts in standby mode, 1.4 Watts when in energy saving mode connected using wired connection and 2.2 Watts when in energy saving mode connected using wireless connection.
So, if you disconnected the printer from the wireless connection and switch it back to the wired connection, the sleep mode problem should be solved automatically. In order to continue using the printer on wireless connection, you will need to access your wireless modem settings and change the wireless network settings to work only on 20 MHz channel. In case you don't know how to do that, please type your wireless modem make and model and I will provide the instructions for you.