I dont see it being easy for the SH, or the Gov. It wont be a stomp.
+ Luffy needs to be within the top 5 fighters for him to be PK, it just makes sense, along with his Genetic Lineage it also makes sense.
+ Assuming Kidd, and Law are suppose o round out the Monster trio (Roger, WB, and Garp) then then they too will have to be of similar Strength and ability to Luffy.
+ I would like to say that Zoro is to Luffy what Rayleign was to Rodger. Along with the fact that he will be the next Greatest Swordsman alive.
+ If Killer is suppose to be Zoro's next big ival when it comes to sword mastery in the SN then he too will have to be pretty damn strong.
+ Keep in mind that as far as Pre-time skip is concerned Basil Hawkins was the "3rd" strongest of the SN if we rank by Bounty. So he too will more than likey end up playing a greater role.
+ There will still be BB and his crew and the other Yonkou, along with the Rev.
We cannot assume that the Pirates will alliance with each other. But we can assume that none of them will side with the WG.
Law, Luffy, Kidd, and someone else (Possibly Sabo representing Revolutionary and taking vengeance for Ace) will be as strong as Akainu, Greenbull, Fuji, and Barsolino. I dont think Garp and Sengoku will participate (my opinion). Boa handock is allied with SH, and besides Mihawk the rest of the worlords arent really that strong, or maybe i should rephrase that, they are not strong enough to be a huge threat. Mihawk will more than likely be fighting Zoro most of the time, unless there fight takes place before then, which im undecided about. Not to mention that more than likely it will be at least 2 SN and there Allys. Mihawk noted Luffys ability to get people to help him, this should not be taken litely when deciding who will and will not help him when it comes to the WG.
Regaurdless it will be an Extreme diff fight. No one will crogstomp anyone. Keeping in mind that WG will have the upperhand most of the fight, as with all of Luffys major opponents. Will he win? Yes. Will it be easy? No. Oh yea he also has all the seakings on his side (well on fishman islands side, but they are his allies).