Our constitution requires Pence to obey the law making it unconstitutional to certify a fraudulent election.
Our Constitution gives Pence no role in the certification process. Certification is done at the state level. In his role as President of the Senate, he is simply required to open the envelopes. It doesn’t even say he “may” open them - it says he “shall” open them.
“The Electors shall meet in their respective states, and vote by ballot for two persons, of whom one at least shall not be an inhabitant of the same state with themselves. And they shall make a list of all the persons voted for, and of the number of votes for each; which list they shall sign and certify, and transmit sealed to the seat of the government of the United States, directed to the President of the Senate. The President of the Senate shall, in the presence of the Senate and House of Representatives, open all the certificates, and the votes shall then be counted.”