Help!! What do you think my beautiful boy is?!!

Given how rare as a breed, Leo's are, I would doubt that is part of the mix (where are you regionally? the breed is more commonly seen in some places, than others). More likely Golden Retriever Mastiff...or Saint/Golden. Might even be some Akita as the brow ridges and heaviness thru the muzzle lend him an Akita like appearance. The feet and such remind also, of an Akita.

If you look at this dog, and your boy's face...they are quite similar, The squareness and "plush" of the muzzle, etc.

Very cute puppy...be interesting to see how he looks a couple years down the road!

Given how much he looks like a Leo, I'd guess Goldeb/Saint Bernard mix.  He's gorgeous.

I don't even have a guess, but OMG he is ADORABLE!!!

Golden/Saint is my guess. Here's some pictures of them:

http://www.dogbreedinfo.com/g/goldensaint.htm

When I first saw it before reading all the other replies I thought he looked alot like "Cleo" our resident Leo in the face.  He is adorable what ever he is!

ETA: he does look like the Saint/Golden on the breed site link.

Partly because of the weight I'm going to say St./Golden -- I had a little mix once who looked SO much like a rare dog mix (a tibetian spaniel) but it would  have been nearly impossible and "Little black dog mix" really fit her better. 

As your boy ages you'll see the personality come out more strongly and then you probably can make your own guess.

 Like with my Luna -- we were TOLD "basset/beagle mix" -- what do i think??  HOUND MIX!!  that's the generous way to say it! LOL

 I'd guess Saint/Golden cross or mix as well. Leos just aren't very common, so I can't imagine there are a ton out there creating mixed breeds. I'm a horse, not zebra person.

He's a very handsome boy though :)

Looking at popularity wise, Saint Bernards are very common either.. not in my area anyway.

I'm thinking GSD/Golden mix.

mehpenn

Looking at popularity wise, Saint Bernards are very common either.. not in my area anyway.

I'm thinking GSD/Golden mix.

 But Saint/Golden crosses are being purposely bred as "designer dogs".

Why? LOL

What possibly would a cross like that do to benefit either breed or the dog kingdom in general?

Okay, so I'm starting.....  I just have to accept that I don't understand it and move on.

Anyway, it's a cute pup regardless of what it is...

mehpenn

Why? LOL...

So the people who produce them can sell them as Leo look a likes.  You know the drill- have a dog that looks like a rare breed without paying the rare breed price. 

Dryfuss, the dog in the televsions series "Empty Nest" was a Saint/Golden mix.  So was the dog that was  in the short lived series 'Father Murphy" (I think that dog was the other one's father).  Anyway- there's another selling point- have dog just like Dryfuss.