Hello, Joe and JDMvW! Thanks for answears, but I think you misunderstanding my problem(may be its because of my bad english :().
My problem is definitely not computer performance. The problem is that running VueScan, which at this time, works with the Nikon scanner, at the same time, somehow blocking at the driver level my flatbed Canon scanner. Something like how audio devices are used exclusively in Wasapi or ASIO mode when other programs cannot use them in parallel. As a result, I cannot use the Canon scanner with other programs while VueScan is running. When I run another program that should scan with a Canon scanner, this program gives me an error, this scanner is busy, although VueScan is currently scanning with a Nikon scanner. As soon as I exit from VueScan, the other program starts working normally with the Canon scanner.
The option, Disable Scanner, is in the VueScan settings, and by design, it is exactly what is needed so that when VueScan starts up, it does not access the selected scanner. Unfortunately, this option did not help me.
Regarding a separate computer, the solution is quite obvious, but in my case it is completely unusable, since I am in the trading floor and I simply do not have place for another computer.