Upload & Sell: On
As a former 1DIIn user (loved that camera!), I echo Vince's information. As long a you have the latest (actually last update) firmware - I seem to remember it as 1.1.2 also, but check to verify - you can use most any size card. Of course you won't get any advantage from things like SDXC or UDMA 7 as the camera doesn't support those protocols (though they can be of value if you use a reader to download images to your computer). In other words you can use slower, cheaper cards.
The 1DIIn's thruput is relatively slow by "modern" standards (6mbs?) so you don't need to buy "fast" cards as the camera can't make use of them. I think the "15ms" cards are faster than the camera. I never put anything larger than a 16GB card in mine. That's a lot of 8Mb pix.
As for brand - that will start a "religious war" around here I used to pay the premium for Sandisk, but long ago moved to Transcend without ever having any problems, and believe me shooting sports with a 1DIV on a newspaper deadline, the cards receive max stress.
Enjoy your 1DIIn - one of Canon's all time masterpieces.