OK, this isn't finished (yet), but here's a small start!

The most immediate questions might be:

• How do bicycles get across the Mackinac Bridge (Lower Peninsula - Upper Peninsula)?
  Answer: you pay a nominal amount, and they shuttle you and your bike across! $5 as of April 2015 (cheaper than a taxi ride of same distance). More here from the Bridge Authority. And here from the Michigan DOT.
• How do bicycles get across the International Bridge (Sault Ste. Marie Ontario to Sault Ste. Marie Michigan?
  Answer: You can ride across on your bike! The toll, I believe, is the same as for autos, though oddly I can't find the information on the website. More here from the Michigan DOT.
• Where can one fly to in the UP?
  Answer: The main commercial airports are at Sault Ste Marie (CIU), Marquette (MQT), Calumet/Hancock (CMX), Ironwood (IWD), Escanaba (ESC), & Iron Mtn. Ford (IMT). These are the ones with commercial airline connectors as of July 2015; most connect to Detroit, Minneapolis, or Chicago. More on the wikipedia page. Of course it always makes sense to search 'nearby airports' on air ticket websites if you are flexible (for instance, this fall I was thinking I'd fly to Calumet again then take the bus to Ishpeming where my bike is, but it turns out that it's cheaper - and more convenient - to fly to Marquette.
• Where can one travel by bus in the UP?
  Answer: There is one bus company operating 'coach' routes in the UP - Indian Trails. It was impossible to just see a bus route map on their website without going through the process of starting to 'buy' a ticket, so I prodded them and almost immediately they added them back! As for their bicycle carriage policy, I didn't see that either so asked and they added that (link is to a PDF on general policies). They state:
  "A bicycle must be contained in wood, leather, canvas, bicycle box, or other substantial carrying case. No bicycles will be transported unless enclosed in any such container. Bicycles transported will be considered one piece of checked baggage. If you have another piece of checked baggage, checking the bicycle will be considered a second checked bag at a cost of $15.00."
  I have taken the Indian Trails bus, at least from Marquette to Hancock (in fall 2014, without bicycle), and found it to be great - much superior to the grim, authoritarian, cattle-car experience of modern air transport!
  I may try the same route this fall (2015) with my bike and panniers as luggage to save a couple days and the maybe too busy 41/28 route.
  According to this map, dated May 2014, and the Indian Trails website there are several lines in the LP as well.
  Here's a little more on John December's website.
• Where do passenger trains go in the UP?
  Answer: Disappointment here - there is no passenger rail in the UP (though Amtrak or whatever might claim a 'route' by linking to bus or air travel routes...)
• Whats the best time of year for biking in the UP?
  Answer: May-October in general; in early May there's still some snow in the woods here and there, esp. on the Lake Superior side, but the roads are fine. Leaves start coming out early May, and there's a profusion of flowers in the woods mid-May to July. Fall colors are on from late September-early October in general. I've camped and poked around in the woods (without snowshoes) early April to late November some years, but best bet is mid-May to Mid-October. The earlier and later times in the year are my preference, because the bugs and tourists are less to none. Summer is busier, hotter, and more with more crowded and expensive motels.
• Where can I get bike parts in the UP?
  Answer: In brief, there are bike shops in the larger towns (you can search the we©, and don't forget hardware stores, lawn mower repair places, etc., in an emergency. I once got some emergency chain links at the Ace Hardware in St. Ignace, and similar places will often have tubes, patch kits, etc. If you're in a real pickle, and need some more specialized part, you might need to stay in-place while the part gets mailed 'general delivery' to you wherever you are (or, if in an area away from post offices, ask a friendly store if you can have the part mailed to them). Be sure to bring the contact info of a trusted mail-order or local shop that will ship for such cases. In my case, I know that Yellow Jersey, in Madison, WI, stocks a lot of the parts I'd potentially need and will ship efficiently and fast in an emergency. Luckily, I never had that emergency (yet), but best to be prepared.
• Where .. what .. how .. ??
  Answer: I should have some more information of interest to potential or on-tour cyclotourists here after a while...
  What am I forgetting?