Hey Stef congrats for me in the past www.thebusschedule.com
online bus schedule for Central America lays your route out well. Last for me spirit.com to CUN mexican directo to Tulum
Chetumal Blize City/Cayes SanIgnacio then jaguartikal.com
Tikal(a must) Guatemala City hedmanalas.com to Honduras.Hotel
hostels basedon budget blackcathostls.net lacasadelmundo.com Yat Balam Copan seagraperoatan.com some budget favs of mine.
Review travel.state.gov crime safety info can get dodgy insure your stuff quotewright.com. Do not share cabs or befriend strangers on buses. The little old ladies are the sneakiest. Money Belt dummy wallet a must for me room safes are not safe every one has a general combo.

Happy Trails!

That's a long trip by bus with only two weeks.

If your budget allows, I'd take the overnight bus from Cancun to Belize City and then fly on Tropic Air from there to San Pedro Sula.

There are also water taxis that operate from southern Belize to Honduras.

Here's a link with lots of information. The water taxi info is towards the bottom of the page.

http://belizebus.wordpress.com/

Tropic Air:

http://www.tropicair.com/

There are a couple of regional airlines in Central America, Taca and Copa, if you want to check flights (expensive but you did want the fastest way).

By land/water...
From Cancun airport, get a bus to Cancun City. You will arrive at the ADO bus terminal where you can change to another ADO express bus heading south. If you arrive late at night, you could get the ADO overnight express bus to Belize City, but if you want to get going immediately, get any ADO express to Chetumal. An alternative from the airport would be get the airport shuttle bus to Playa del Carmen, but in Playa you have to change bus terminals to get the express bus to Chetumal. If you want to stay overnight in this region, I'd choose Playa rather than Cancun.

In Chetumal, you have 2 options...
1. if you want to see a bit of Belize, get a water taxi to Ambergris Caye (or continue to Caye Caulker) and stay there. Continue by water taxi to Belize City.
2. if you want to get through Belize as quickly as possible, get a Belizean bus to Belize City (trip time about 4 hours & BZ$12). The Belizean buses depart from the Neuvo Mercado (New Market) near the ADO bus terminal.
3. arrange to be picked up by one of the transfer services and taken to BC. It's more expensive, but quicker and more comfortable.

In Belize City, you have a few options, but timing is a concern.
1. Tropic Air flight to San Pedro Sula -- departs BC Mondays, Wednesdays & Fridays at 8 am.
2. Water taxi from Belize City to Puerto Cortes, Honduras. Trip time is a few hours, but the boat departs only on Saturday mornings at 9 am (BZ$145).
Both these would be good options if you arrive at Cancun on a Friday and get the overnight bus that arrives in BC at 6 am.
3. There are other water taxis from Dangriga and Placencia, but these option involve a long bus ride and these water taxis depart only on Friday mornings.
4. There is a weekly express bus to San Pedro Sula -- 12 hours & about US$70.

More details are on the Belize Bus & Travel Guide:
http://belizebus.wordpress.com/

thank you very much for the replies, i'm a wee bit less worried now...despite being a long journey, sounds somehow achievable.
will look at all the links you've sent; travelling by land/water is our preferred option at the moment, but we'll check the flights too, just in case...

the main issue for the leg belize-honduras on water seems to be the weekly schedule of the boats; although, considering that we will arrive on saturday to cancun, in theory we could have 1 week to get to Belize City and catch the sat boat to Honduras and spend the other week there.
well, at least i will..she will carry on visiting the rest of the country whilst i'll be flaying back to London.