Of course we know Thanos is most likely not going to be Starlord's father, here are some quick reasons why Thanos could be his daddy.
1.Starlord's Alien like tendencies
In Guardians of the Galaxy, Starlord was able to hold the infinity stone for a long time alone, no mortal could do this and Marvel could totally use Thanos as an explanation for this.
2. Starlord had purple skin
In the picture below, you should be able to see Starlord's blood is purple, everyone else has a dark red color in the film. Why would Starlord have purple blood, or was it an editing error? We'll find out in the sequel, those are all the reasons Thanos could be Starlord's dad.
The Collector doesn't need reasons, he and Starlord simply have a similar clothing style(The Collector's style is more vintage and fancy), they share a devious and traitor-like personality yet there is good inside, and The Collector seemed to give Starlord a familiar look as he walked in the room but quickly got to business.
Well, thats all for now, catch you later ;).