Mr. Sharma may be late but I am sure Mr. Gupta ......................

A: This implies impossibility, but it doesn't fit with the sense of assurance conveyed in the sentence. It's possible for Mr. Gupta to be late, so "can't be" doesn't work here.

B: This is the correct choice. It expresses the idea that the speaker is confident that Mr. Gupta will not be late. It aligns with the sense of assurance in the sentence.

C: This implies a hypothetical situation or a conditional statement, neither of which fits the context. "Would be" suggests a future event based on a condition, but there's no condition provided in the sentence.

D: This is incorrect because "are" is the present tense form of the verb "to be," but the sentence requires a future tense to indicate Mr. Gupta's lateness.

Therefore, Option B is the correct answer.