Canadian citizens do not require O or P visas to enter the U.S., but do require approval from the USCIS. Canadian permanent residents (landed immigrants) DO require visas, as do all third-country nationals (those not from the U.S. or Canada) entering the U.S. from Canada.  Canadian citizens need simply present themselves at a port of entry or pre-flight inspection location with proof that USCIS has approved their O or P classification. If the petition has been approved, the computer system will contain a full record of that approval, but the best proof remains an I-797 Approval Notice. An alternative is a USCIS fax. As with consulates, however, for various reasons faxes do not always find their mark. As a precaution, always provide the alien with a full copy of the underlying petition. Otherwise, though, there are no applications as such or visa fees if visas are not required. Note that all U.S. Customs and Border Protection (CBP) personnel can quickly access approval information once entered into the system, so it is inexcusable for a CBP inspector to refuse to admit an alien who does not require a visa simply because s/he lacks the original, or even a copy, of the I-797 approval notice because the inspector cannot find the fax or, worse yet, refuses to look for it. 

Canadian nationals or permanent residents applying through land ports of entry receive I-94s only if they pay a $6 fee. If not, the CBP is supposed to stamp their passports with the entry date and classification in which admitted. It is then up to the alien to avoid staying beyond the authorized period of stay. In the present climate, Canadians should obtain some proof of the time, manner, and status awarded at time of admission. For this reason, we recommend paying the $6 fee or at least ensuring that CBP stamps the passport.