You might not want to do that until they process your rebate. If they have some way of checking your activation during the rebate process and they see you already cancelled, they might be like... oh, thanks for the money - sucker!
While this deal looks appealing on the surface, keep in mind that this exact tablet sold for $60 at TigerDirect.
The software alone is $49.98
The rebate is $70, making it a $20 MM (less S&H).
So essentially: $60 (bundle discount tablet) + $49.98 (software) - $70 = $39.98
Good point on the activation!