it will still clear.
There are 2 parts to this:
1) Crossing the cheque in the top left makes it "account payee
only", means that it can only be banked into an account. If u dun
cross, u can withdraw cash.
2) Crossing (cancelling) the "or bearer" means only the person
whose name is written can get the money. If u don't cancel it,
ANYONE (i.e. the 'bearer') can take the money.
So if the cheque is written to "FireIce" for $1,000,000, but u dun
cross the top left and cancel 'or bearer', I can take it, walk into
the bank, and get $1,000,000 in cash (in theory anyway).