Hello Robert. To add to what Mason Jar has said.
Travelling Hwy #401, take a side trip into Brighton to look at Memory Junction Museum
http://www.memoryjunction.netfirms.com/ This place is right next to the CNR Kingston sub double-track main line. Instead of getting back on Hwy #401, take Hwy #2 all the way to Napanee. You will be travelling alongside CN's Kingston sub (double-track) and CP Rail's Belleville sub (single-track). Take a side-trip in Belleville to CN's Belleville yard - the largest between Montreal and Toronto.
Then make your way to Smiths Falls. You can get there via Hwy 15 at Kingston, or you can travel to Brockville and exit at Hwy 29. My preference would be at Brockville as you can take a side trip to the VIA station, grab an ice cream cone and maybe watch some of the trains go by on CN's Kingston sub. It's also where CP Rail's Brockville sub from Smiths Falls comes in. You could make your way down some of the back streets and take a look at CN's Manitoba Yard. If you're into railway history, you might find your way down Church St to the intersection with Buell's Creek where the Brockville, Westport & Sault Ste Marie Railway ended.
As you travel up Hwy 29, you will pass by Forthton on a large curve. To your left (west) you might see the old BW&SSM Forthton station, built in 1886, under renovation. However, if you blink, you will miss it.
Arriving in Smiths Falls, make your way to the Smiths Falls Railway Museum
http://www.sfrmeo.ca (if you've got kids, you might first want to make a side trip to the Hershey Chocolate factory and stock up on some chocolate bars (price is about 10 cents each)). This should be worth a couple of hours as you wander through the cabeese and station, take a look at 4-6-0 #1112 and Alco/MLW S-4 diesel, and a tour through the dental car. Perhaps they might have the handcar and speeder running that day.
Next, make your way to the VIA station which has a nice bench for watching CP Rail's, VIA Rail's trains go by. There's usually a switcher or two switching cars in the yard. Around 1:30, 4:00, and 6:00 there's always some passing movements of the Ottawa-Toronto VIA trains as one comes off the VIA Smiths Falls sub, makes their way across the CP Rail tracks and onto CP Rail's Brockville sub (or visa-versa). CP Rail's XPressway usually arrives around 3:30 which makes for some interesting train movements with the VIA trains.
From there, you can head into Ottawa to your digs. I would suggest heading to Ottawa via Merrickville for a visit to Larkspur Line - the best HO scale model railroad shop in Canada
http://www.larkspurline-trains.com/ . Pat and Jeff Trew are always very helpful if you can't find what you're looking for. You also have the added benefit of seeing a bit more of CP Rail's Winchester sub and the beautiful double-tracked bridge over the Rideau River at Merrickville.
If you're adventurous, you might try making your way down the back roads to Bedell which is just south of Kemptville. This is the junction with CP Rail's Winchester sub and their former Prescott sub. The Prescott sub is the former Bytown & Prescott Railway built in 1854 from Prescott to Ottawa.
A trip to the Canada Science & Technology is a must
http://www.imagescn.technomuses.ca/railways/index.cfm . As Mason Jar has mentioned, the Shay is usually running on Wednesday and Sunday afternoons (free rides). The train is operated by the guys from the Bytown Railway Society. Then there's the locomotive hall inside the CSTM which is a must, in addition to what's outside on the grounds.
On Saturday morning, the boys from Bytown (that includes me) get together at the CSTM to work on their equipment (TNVR #10, CV steam crane and boom car and tender, CPR caboose, TNVR #27, CNR passenger car #4977, CNR baggage car, etc)
http://www.bytownrailwaysociety.ca/equipment.htm . Simply follow the tracks back into the large building. Ask for me and I will show you what's hidden away.
Ottawa Central Railway operates out of the Walkley Yard which is off of Hunt Club and Albion Roads. This is always a good place to see some Alco/MLW RS-18s. However, the place is under tight security so don't go wandering around.
Then there's always Ottawa's O-Train - a real deal for a couple of bucks, VIA Rail's Ottawa Station where trains leave for Montreal or Toronto. Unfortunately, the Hull, Chelsea & Wakefield steam train has been sidelined for the summer due to a mud slide right next to the tracks. There are rumours of an impending deal which might see the train running again this fall.
Of course, we haven't got to the Parliament buildings, the changing of the guard, the Rideau Canal, the other museums, the parks, the Ottawa River, and all the other sights that will keep the rest of the family very happy and very glad that they allowed you to take these side trips.
As you gaze over the Ottawa River from the Peace Tower of the Parliament buildings, that beautiful bridge downstream to your right (east) is the Alexandra Bridge that carried trains across the Ottawa River from the Union Station located across the street from the Chateau Laurier. When you visit the War Museum, you will be travelling across the old Canada Central (CPR) and Canada Atlantic (CNR and JR Booth) railway yards. So, before you go, take a look at some of those old railway history books. You will be travelling right across where those photos were taken.
Oh yes. One last thing. Your Canadian Trackside Guide published by the Bytown Railway Society. Don't leave home without it!
Bob M.