Should I avoid a switching frequency close to my target SPI or CAN frequency?
If the regulator were that bad it'd screw up the board operation no matter what.
If you had a radio in there, then having a regulator switching at the RF frequency or a sub-multiple of it could be an issue (as could having a microprocessor clock close to a frequency you care about).  But CAN and SPI aren't going to notice anything that won't generally make the whole board unable to function.