Making pesto. Can I use soynuts or sunflower seeds in stead of pine nuts?

Sunflower would work well but soy nuts probably wont. Soy nuts might disintegrate when processed in a food processor or morter and pestal whereas sunflower seeds have the right texture. Watch the salt if you are using salted sunflower

Pine nuts are the classic but I have made it with walnuts and maccadamia nuts

i would go with the sunflower seed (toast them before making it), it will be a pesto with a twist, but i don't see any problem with that.

Also try: hazelnuts, walnuts

I wouldn't use soynuts, possibly toasted sunflower. Try walnuts or hazelnuts or else just do without, the basil oil and garlic will suffice.

then it is not pesto. pine nuts are the flavor of it.

you can, but the taste and consistency may be off, so you may need to add more, or less olive oil!

Good luck.