Please pardon the LONG post, but I think what you're referring to is section 123.17(b) of ITAR (Exports of firearms and ammunition.), which reads:
"Port Directors of U.S. Customs and Border Protection shall permit the export without a license of nonautomatic firearms covered by Category I(a) of § 121.1 of this subchapter if they were manufactured in or before 1898, or
are replicas of such firearms."
http://www.pmddtc.state.gov/regulations_laws/documents/official_itar/ITAR_Part_123.pdf
That Category 1(a) they refer to in that last section is the ITAR Section 121, also known as the U.S. Munitions List, and that section describes:
"CATEGORY I—FIREARMS, CLOSE ASSAULT
WEAPONS AND COMBAT SHOTGUNS
(a) Nonautomatic and semi-automatic firearms to caliber .50 inclusive (12.7 mm)."
http://www.pmddtc.state.gov/regulations_laws/documents/official_itar/ITAR_Part_121.pdf
That means my Chaparral 1876 Win repro in .50-95, & Armi Sport Spencer 1865 in 56-.50, were just as easy to get across as my Shiloh Sharps 1874 carbine in .45-70. I have no idea about shipping directly, as I live in a border-town & went through a U.S. FFL for several reasons. The FFL got me the items locally, at which time a friendly verifier can take a look at them with me & confirm the info. I didn't want to chance some faceless flunky freaking out somewhere & refusing the items, or calling the RCMP over what IS a legal act, so I preferred to do it face-to-face where I could answer questions & produce reference documents in support.
Now, the rifles may be exempted from ITAR export restrictions, but the ATF still considers them firearms, meaning it's a felony for us Non-Immigrant Aliens to be in possession of them on U.S. soil (except under some circumstances that didn't apply in my case), and for an FFL to give us possession of them. The FFL may directly export them, which in the context of a small border-town, meant driving a pick-up truck to the Canadian side to hand them over to me where I waited at the bridge plaza (hint: calling the local CBSA office, giving them a head's up, & asking if they have any preference on how to proceed is a great idea to smooth the process, they may also tell you about quiet times with minimal waits).
The firearms must be declared when coming over, and CBSA staff will need to confirm the info, and that you are in compliance with transportation regs. They may also want to check out the neat rifles, but that's another matter. (hint: be patient. Not every customs officer knows every firearms reg like the back of his/her hand. Any more than you may know everything about agricultural product restrictions or excise issues.) I was told that everything was in order, that I would have to pay the PST/GST on them, but wouldn't be able to take them home right away, until they were registered. The guy I spoke with was pretty surprised when I said that they already were.
I had faxed the registration applications (CAFC 998 form--
http://www.rcmp-grc.gc.ca/cfp-pcaf/form-formulaire/pdfs/998-eng.pdf ) to the Registry already. Under block (A)1 I ticked off "NEWLY IMPORTED FIREARM", and in the box notes field I typed "Firearm awaiting importation clearance from CBSA".
I called up the Registry the next day & asked about the status; it was processed already. They can't/won't fax you the Regt Cert, but will give you the number. I listed the Regt Cert numbers on the application forms, and produced them for the CBSA staff. One guy told me they needed the ORIGINAL Regt Cert to allow import, so I pointed out references from CBSA documents to him that they did not, and invited him to access the Registry database to confirm the PROOF OF REGISTRATION that I had provided him. In the end they didn't bother. I didn't even have to provide my last-resort 'trump-card' in the form of Appendix F (REQUIREMENTS FOR CUSTOMS RELEASE) to CBSA memorandum D19-13-2 (memorise this number, link below), which allows release on proof of valid licence. Everyone was polite, friendly, efficient (yes, really), and it was all over in about 20 minutes. I hear it takes longer to import ATV's?
Incidentally, non-restricted firearms can be imported into by individuals Canada without an International Import Certificate (IIC), as per CBSA memorandum D19-13-2, under Tariff 9898.00.00
http://cbsa-asfc.gc.ca/publications/dm-md/d19/d19-13-2-eng.pdf
All necessary firearm info is supposed to be noted in the B15 Casual Goods declaration form, and it's probably a good idea to remind them to include at least the make/model/serial#/Regt Cert# info, and keep your copy, in case of any future questions.
Lastly folks, a little rant: ALL this info is available for free, on the 'net! Don't listen to me, look it up yourself & be sure. Would you take legal advice from some anonymous 'StumpHumper6969' on bubbashouseofguns.com? I wouldn't. After asking several different cops, and border staff in Canada & the U.S., and getting as many different answers as people I spoke with, I said to hell with it & researched it myself. It took a long time, but much less than the time I'd spend in a U.S. prison for any number of felonies if I hadn't looked it all up. It may seem a waste of paper, but I also took the time to print out many/most of these reference documents to have on me when importing them. It helped. NOBODY asked me 'why do you want to bring something like that into Canada', but two guys commented on me 'having done my homework', and 'having everything well in order'. You learn the regs, and you help yourself. Oh yeah, that Shiloh carbine is SWEET!