Tire Change Compatibility
Save your money and get a used bike instead (look for bike shops in your area that sell used bikes, or craigslist or something). 230 dollars should net you something decent from the 80s or 90s, along with some accessories (helmet, locks, lights, etc.). It'll be much higher quality than what you're looking at (the bike you've linked is bso-ish), and older road bikes have much larger tire clearance normally than newer bikes.

One of the big problems with buying your first bike online is sizing -- not everyone fits the sizing charts bike manufacturers may publish. And you don't get a test ride online to know if it will fit you well. 

The C&amp;O canal towpath just has a bit of gravel on it, not much terrain toughness. I'd not worry about knobs, just 28c+ tires. As for sizing, you have to try the tires with the particular bike, especially with a road bike. Normally with modern road bikes, you can maybe go 1 tire size up with a smooth tire compared to whats originally spec'd. You've gotta check the tire clearance to see if the tire will fit (also note that two new tires will run 40+ dollars on the low end). So, I'd conjecture that the 28c tire won't fit.