Alaska "join me latter" luggage

what size of luggage is recommended for the cruisetour luggage that goes to the lodges?

Whatever you want. We had a 28" suitcase going from lodge to lodge and sent our rolling garment bag ahead to the ship.

what size of luggage is recommended for the cruisetour luggage that goes to the lodges?

https://www.princess.com/learn/faq_answer/cruisetours/cruisetours_alaska.jsp

Packing for your Land Tour

Cruisetours involve many modes of transportation including motorcoaches, trains and sightseeing vehicles so make sure you take only the things you need to ensure comfort for you and your fellow travelers. There are different types of bags to consider for the land portion of your cruisetour.

Hand-Carry Tote/Backpack

• You'll want this bag with you every step of the way, so include only the essentials.
  
• Items to pack in this bag include travel documents, photo ID, important medication, toiletries, camera, and any extra layers of clothing such as jackets or hats.
  
• Your hand-carry tote bag should be a size that is comfortable to carry and should be able to be stowed under your seat. We recommend soft-sided tote bags or backpacks no larger than 17" x 14" x 4" with a zip enclosure.
  
• Wheeled carry on cases that are used to carry-on luggage on airlines are too large and are not suitable as hand-carried luggage on motorcoaches and trains.
  

"Join Me Tonight" Luggage

You are allowed one piece of "Join Me Tonight" baggage per person on the land portion of your cruisetour. You will simply pack one bag and place luggage where instructed. Our handlers will pick it up and deliver it to your room at the next overnight location on your land tour.

• This bag will be transported separately from you and will not be accessible during transit.
  
• Items to put in this bag include clothing, sleepwear, nonessential toiletries, extra shoes and anything else you might need at your hotel but do not need access to during the day.
  

I have taken a backpack, a regular size (airline checked) bag to the lodges and sent my carry on ahead to the ship. You don't have to worry about weight until you're flying.

what size of luggage is recommended for the cruisetour luggage that goes to the lodges?

This is the "Join Me Tonight" luggage.

The "Join Me Later" luggage is what meets you at the ship in your cabin at the end of the land tour (assuming you tour first and cruise second).

You can read more about this in my land tour report at https://boards.cruisecritic.com/showthread.php?t=1727858