Supporting Evidence Question for Child out of Wedlock

[p0p0]

I am interested in starting the green card process though my father (who is a US citizen). I am 21 years old so apply to the family class (not immediate relative). I am a Canadian citizen. My father's name is not on my birth certificate, and my parents were never married so as far as I understand the following applies:

4. A child born out of wedlock and you are the father: If the child was not legitimated before reaching 18 years old, you must file your petition with copies of evidence that a bona fide parent-child relationship existed between the father and the child before the child reached 21 years. This may include evidence that the father lived with the child, supported him or her, or otherwise showed continuing parental interest in the child's welfare

I'm not really sure what evidence they are looking for. I have emails dating back from 2004 referring to financial support, but no real records of the transactions. Much of it was given in cash or cheque. I never lived with him, so I don't really have any proof on that end. Should I get a DNA test? (I don't have his last name).

If anyone could provide some information on this matter I would highly appreciate it (I am finding the website hard to navigate for this issue).

Thanks!