Can I stay in the US for leisure from June - Oct 1st under B2 visa until H1B takes effect?

As you are a Canadian, you do not require a visa to enter the United States for visiting purposes. If you have a valid reason for being in the US for visiting purposes such as visiting with your boyfriend, you can explain that to the inspecting officer upon your entry with a Canadian passport. Similarly Canadians are not required to have H-1B visas put into their passports. At the appropriate time, you can approach the port of entry with your I-797 H1B approval and requested admission into the US to take up your H-1B position. You may of course have to explain what you were doing in the United States from June-October 1.Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.