There is no TWAIN 64.
It is recommended you use the scanner software to scan, save to a location then open in Photoshop.
This method is also more time efficient as you can use PS for someting else while scanning.
Most older scanner drivers are 32 bit and can run with TWAIN 32 bit in Ps 32bit installed at same time as 64bit...
So scan using Ps 32bit, save as .psd, then open in Ps 64 if you need more than 2GB RAM ...or just use in Ps 32bit if RAM under 3GB is OK
That's what I am doing now, scan in PS 32 bits and then open in 64 bits because in the latter version I have all my preferences and workspace set up the way I like.
Still I keep being a little curious who is to blaim and at this point I suspect it is Canon...
Microsoft and scanner makers decided that there would be no TWAIN 64 on Windows, so there is no TWAIN support in 64 bit.
In 32 bit you can use TWAIN, Wia, or the stand alone scanning application.
In 64 bit, it's Wia or stand alone only.