Canadian scholars do not need a visa to enter the United States, however you must be sure to complete your I-94 record with the U.S. immigration official at your point of entry to the United States. If you enter the U.S. by land, you will be given an I-94 record. If you enter by air, your I-94 record will be entered into the online system. You will need to print out your I-94 record upon your return to the U.S. as evidence of your legal status. In both cases, you will be charged a small fee to process the I-94 record.
As U.S. immigration inspectors are accustomed to admitting Canadian citizens as visitors and not scholars, it is your responsibility to make sure you are granted the correct immigration status when you are entering the U.S. If you are admitted as a visitor (or tourist) without receiving an I-94 record noting your immigration status (e.g., J-1, H-1B, TN, etc), you will have to return to Canada and re-enter a second time.