Will you for sure to join us?

The following justification is meant for the one who is in support of the grammar behind the interrogative sentence: "Will you for sure to join us?"

The word sure is both an adjective and an adverb. The word surely is also an adverb. The word sure is used as an adjective in both the following sentences:

1. "Will you for sure join us?" which is the same as "Will you join us for sure?"
   
2. "Are you sure to join us?"
   

Both the sentences are grammatically correct. According to the Oxford Dictionary, there is no way you are above which, explains the usage of the phrase for sure and the idiom be sure to do something in the following extract verbatim:

IDM be sure to do sth used to tell sb to do sth: Be sure to give your family my regards. for sure (informal) without doubt: No one knows for sure what happened. $I think he'll be back on Monday, but I can't say for sure. $One thing is for sure - it's not going to be easy.

In case you don't understand which sentence uses which form, the second one uses the idiom.

And just because an American Professor typed it out in an e-mail to you doesn't make it right, because nobody is perfect. Just like the occasional blunders in your Telugu and Oriya!