Bhai Kahn Singh Nabha has done a great task of explaining Gurmat philosophy in this book.
There is some common ground between Gurmit and other faiths, but the fact remains that the Sikh faith is independent in its own right...
A great book in English giving counterpoints to arguments made by Hindus - http://discoversikhism.com/sikh_library/english/sikhs_we_are_not_hindus.html
Also if anyone wants to share any other arguments made by others we can give counterpoints if needed.
ਬੁਰਾ ਭਲਾ ਕਹੁ ਕਿਸਨੋ ਕਹੀਐ ਸਗਲੇ ਜੀਅ ਤੁਮਾਰੇ ॥੧॥ ਰਹਾਉ ॥
Tell me, who should I call good or bad, since all beings are Yours? ||1||Pause||
Ultimate Doer is "Kartapurakh"