All it means is that the cheque has two little lines that go vertically through the lines that you fill in (payee and amount) and it usually says something like Payee only or Account Payee along one of the vertical lines. This means that it can only be cashed by the person or company the cheque is made out to. If you have an uncrossed cheque then the payee can sign the back and anyone can pay it into their account. Shouldn't make any difference to the company receiving it unless they figure one of their employees will nick the cheque!

Anyway, I think all cheques are printed 'crossed' by the issuing bank these days so I shouldn't worry about it. I haven't seen uncrossed cheques for donkeys years and it is very old-fashioned to specify this (you used to have to manually 'cross' the cheque.

Could be different in Canada though. So, in the event of your cheque not having this stuff printed on, just draw two vertical lines around 1cm apart down through the payee and amount lines and write one of those phrases down one of your drawn-on lines.