MoaningOdin

I can find him some busy work, the garage needs cleaning and sorted, the boy's rooms need rearranging, the upstairs bathroom could use some fixing up. I think I can figure out some stuff. I wasn't aware it would be that long, I saw somewhere that he could work after 6 months so I hadn't done anymore research. I'm glad I asked today though, now I can try to prepare some projects for him to do. 

He will need to obtain his travel and work permits first. If he flys back to Canada without them, he will not be allowed back into the US

You cannot get married prior to entering the US on the K1 Fiance visa. He has to enter the US unmarried, then get married within 90 days of entering and file AOS along with EAD/AP. He cannot leave the US or work until the EAD/AP are approved, which currently takes 6-10 months, sometimes longer. Well, actually he can leave, but he cannot reenter the US. If he wants to come back to the US after that point, you need to file the CR1 spousal visa and that will take about another 12-14 months. 

Once you get married he can of course leave US.
 
He won't be allow back in the US though. He CANNOT leave US without green card or Advance Parole in hand. None of those will be available immediately. It's going to be at least 4 - 6 months just for AP.
 
 

Have you considered a CR-1?
Every couple has their own priorities, and each couple must decide which visa is better for their situation.
K-1
    Slightly faster arrival in the US (currently about 3 months sooner)    
    More expensive than CR-1    
    Requires Adjustment of Status after marriage (expensive and requires a lot of paperwork)    
    Spouse can not leave the US until she/he receives approved Advance Parole (approx 5-6 months)    
    Spouse can not work until she/he receives EAD (approx 5-6 months)    
    Some people have had problems with driver licenses, Social Security cards, leases, bank account during this period    
    Spouse will not receive Green Card for many months after Adjustment of Status is filed.
  
CR-1
    Slightly slower arrival in the US (currently about 3 months later)
    Less expensive than K-1    
    No Adjustment of Status(I-485, I-131, I-765) required.    
    Spouse can immediately travel outside the US    
    Spouse is authorized to work immediately upon arrival.    
    Spouse receives Social Security Card and Green Card within 2 or 3 weeks after entering the US    
    Opening a bank account, getting a driver's license, etc. are very easily accomplished with GC, SS card, and passport.
    Spouse has legal permanent Resident status IMMEDIATELY upon entry to US.

You will find lots of good information on this web site, he should be aware he will not be working for a long time.

As stated above by @Roel, he won't be leaving the US or working for 4 to 6 months after you file for Adjustment of Status.  After that, he will have to make sure he keeps his US residency.  

To clarify, he won't be able to work in the US either, until his EAD is approved, which could be 6-10 months, some cases reported 12 months +. He can't travel outside of the US either, for the same amount of time. So unless you have a lot of projects lining up around the house for him, he's gonna be bored out of his mind.