How can I pair my Magic Trackpad with multiple Macs?
No, it can only be paired to one computer at at time according to Magic Trackpad Manual. You would need to un pair and then re pair it to another computer in order to use it on both computers.

Here's the extract from the manual: 


  After you pair your Apple Magic Trackpad with a Mac, you can pair it again with a different Mac. To do this, you first remove the existing pairing and then pair the trackpad again.