Can I run any form of it with a 1tb WD Drive and a 3 TB Seagate Drive?
raid needs 2 identical drives.
they need to be the same capacity
They don't have to be the exact drive, just the same capacity. So in the OP's situation it won't work.
They don't even need to be the same capacity, but the 3tb will lose 2tb to be partitioned to match the 1tb.
You can use softwhere raid with 2 mismatched drives but the lager drive needs to be partitioned to the same size as the smaller drive.
So you will be wasteing 2tbs of space on the 3tb drive.
Hardwhere raid it realy depends on the controller.
Just buy anuther 1TB to use for raid (or buy 2 and have a nice raid 5 set up between 3 discs giveing a bit of speed boost and some redundancy HDDs are fairly cheap now)