The phrase "most forsure" is a colloquial way of saying "most definitely" or "absolutely." There are many synonyms for this phrase that convey the same level of certainty. Some alternatives include "without a doubt," "certainly," "positively," "undoubtedly," "indubitably," and "surely." Other phrases that convey the same tone include "for sure," "no question," "beyond any doubt," and "without question." Whether you're trying to emphasize your certainty about a particular matter or simply looking for an alternative way to express your confidence, there are plenty of synonyms to choose from.