Canon 70D max supported SD card size

I just took a very quick look at the manaul online, and right there on page 3, it says:

Compatible Cards

The camera can use the following cards regardless of capacity:

• SD memory cards
• SDHC memory cards*
• SDXC memory cards*

*UHS-I cards supported.

I would advise having a read through the Wikipedia article on SD cards. Card capacities are not the main factor in determining compatibility. SD cards have gone through a number of generations – SD (SDSC), SDHC, SDXC, SDUC – and newer generations are not necessarily backwards-compatible. There are also different bus interfaces – Default Speed, High Speed, UHS-I, UHS-II, UHS-III, SD Express.

There is additionally this relevant FAQ on the Canon website:
What Memory Cards can be used with the camera? (EOS 70D)

If the card you are considering fulfils the compatibility criteria that Canon mentions, then I see no reason why you should continue to assume incompatibility.