It's hard from your description to tell where you are in NB, but here's my experience from our first year on our property near Fredericton.
"Last frost" date of mid-May, had our final frost in mid-June (killed our crab-apple blossoms, but somehow our tomatoes survived).
We had tomatoes growing into late September/October. Only lost them because I forgot to cover them one night and the frost got them.
This summer was hot and dry - more so than previous years. Our property is south-facing so we get the worst of it but the past 3 years have been unseasonably warm and dry in the province.
For today's context: We're doing our first big planting mid-May, two weeks earlier than last year. A lot of nature's signs have been pointing to an earlier season start, and a later season end. Our spring this year has been very strange, and I worry we won't have the same kind of season in the next 5-10 years.
As for hazelnuts: yes, yes yes! Beaked hazelnuts are native to the province and you may find some at forest edges around your property. More productive varieties should do just fine.
For fruit: plums are your friend (at least more artic varieties), and apples do well (although better with North-facing exposure). We have many volunteer apple trees in our forest thanks to the prolific deer and orchards around us.
Berries: there are about a dozen native berry bushes in NB, so you're good to go on that front for most berries you would want to have. I'm jealous of your wild blueberries!
Timber-trees: Think about planting some red oak in the future. The climate is changing and it is drastically affecting the makeup of the forest in the province. The Acadian Forest is a mix of boreal and northern hardwood. The boreal sections are being pushed further north and the composition of the forest will likely see a big shift in the next 10-20 years.
We're just getting started in our journey. Let's grow together in NB! :)