Here are some possible translations depending on the context:
Formal:
* I am sure you...
* I am confident that you...
* I am certain that you...
Informal:
* I'm sure you...
* You must...
* You're bound to...
Example:
* French: "Je suis sûr vous allez réussir."
* English: "I'm sure you'll succeed."
The best translation will depend on the specific sentence and the desired tone.