This is basically the same trip that Emanoh reported on in his trip report. My Dad and I put in on the North Branch of the Portage River in the downtown of Pemberville. We were both paddling our racing C-1s. The trip was 22 miles from Pemberville down to Oak Harbor.
From Pemberville past Woodville the river is slow to moderate current with occasional riffles. Past Woodville and before Elmore, you begin to get numerous small islands and easy rapids on the river. There is a tiny low head dam before you get to the Ohio Turnpike. There were slots in the dam and we were able to run through the chute. At the water level we paddled, the rapids at the turnpike weren't bad. I had thought we might have to portage around the rapids with our carbon fiber boats, but we were able to pick a route through this area. The only place we had to portage was the Rt. 51 bridge rapids in Elmore. Below Elmore is a broken down dam that you can easily run though one of two slots.
Here is one of the water gauges located close to Elmore - http://waterdata.usgs.gov/oh/nwis/uv?04195820 (it was at 2.95 when we did this trip). With my racing canoes I've always found that I wanted the gauge height to be above 2.6 feet. At the lower end you can paddle a lot of the river, but may have to briefly get out for an occasional shallow riffle. It took us just over 4 hours to paddle the entire distance.
You can stop in the towns of Pemberville, Woodville, or Elmore if you need to get something to eat or drink.
From I-75, you can take OH 105 to Pemberville. Rt. 105 runs along the river from Pemberville to Oak Harbor.
Canoeing and Kayaking Ohio's Streams by Rick Combs.