"If you are declaring more than 3 firearms, please complete and attach a Non-Resident firearm Declaration - Continuation Sheet (CAFC 910). If you need a continuation sheet, you can call us at either 1-800-731-4000 in Canada and the USA or at 506-624-4380 outside Canada and the USA and we will send you copies. These sheets are also available at any Canada Border Services Agency office."
Bottom line, ......call and request a 909 and a 910 form. And have a US Customs form 4457 for re-entry.

"A Stranger is a Friend we haven't Met"