When you download from Canon Creative Park make sure you choose the paper size you want to use. There is a choice for A4 or USLtr. A4 is a little longer and narrower than USLtr. A4 is the standard outside of the USA and is not readily available in the USA.
110# index/199 gsm or 65#(or sometimes 67#) cover/177 gsm are two of the most used paper weights. The weights in pounds or
grams per
square
meter will be on the packaging. You will most likely catch the paper model making virus so go ahead and buy some of both. Any store that sells office supplies or craft supplies with have that cardstock.
Try to build the model using the 110#/199gsm cardstock. I have built a few of those Canon Creative Park models using that weight and it works out OK.
