。
The max we can load is 100 kilos.
Literal
Load-[potential-られる] [nominalizer-の] [topic-は] 100 kilos [subject-が] max is.
乗せられる is the potential form of 乗せる ('to place on, to load'), so 'can be loaded.' The の is a nominalizer turning the verb phrase into a noun: '(the amount) that can be loaded.' The 'the X is Y' shape is the classic Japanese cleft: topic-は ... が predicate, with は on the scope-setting topic and が on the focused quantity. マックス is a direct English loanword for 'max.'