I've purchased lots of army surplus clothing and field gear from the States with no issues.
Sometimes, packages are inspected by CBSA at the border (x-ray or physically opened) but as long as you're not importing ITAR-controlled goods or prohibited items, you shouldn't run into any issues. Probably more information than you need, but it may be of interest:
Quote:
Examples of controlled goods, technology, and software (list is not all-inclusive):
Toxicological agents*
Nuclear materials and technology
Lasers and Sensors
Night vision equipment
Select agents (and other pathogens)*
Arms and ammunition
Explosives Detection Equipment
Chemical warfare precursors*
Semiconductors and microprocessors
Telecommunications and encryption software
Missile technology
Navigation and avionics
Marine vessels
GPS technology
Countermeasure technology for controlled goods
Endangered Species
Body armor and protective gear
Fingerprint and identification retrieval
Oscilloscopes
Gas centrifuges
Mass Spectrometers
High strength materials
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Quoted from
https://export.duke.edu/exporting/controlled-items
Edited to add: beware of eBay's Global Shipping Program which basically charges double the cost of United States Postal Service (USPS). I always choose the latter.