Henry Deacon plays a prisoner in Warehouse 13 who also leads a religious sect.
The episode "For the Team" finds Artie experiencing stomach pains due to his appendix growing back. In the show Eureka, Saul Rubinek once played a biologist who ends up with regenerative abilities. Although it turns out that in Warehouse 13, the regeneration was intentionally induced, unlike in Eureka, where it was purely accidental.
Pete also hopes H.G. didn't pick up her knowledge of forensics by watching Dexter.
Like Val Preston, Steve Valentine really is an accomplished stage magician in real life.
Brent Spiner playing two versions of the same character, one evil, one... well, maybe not nice, but considerably more level-headed, once the real Brother Adrian is released from the painting along with the rest of the Order of the Black Diamond. Data and Lore, in other words.
When it's revealed that the history professor played by James Marsters is the Count De Saint-Germain, they ask him how he still looks the same if he's so old, Pete asking him specifically if he's a vampire. He dismisses this, saying "vampires are for gothic novels and teenage girls."
Finding H.G. Wells (played by Jaime Murray) working in a forensics lab makes Pete quip that he hopes she didn't learn her lab skills from Dexter.
Claudia and Fargo keep switching positions at the end of the first act of "13.1"; one is in the chair while the other is leaning over the desk and then back and forth.
At the end of "Personal Effects", when the doctor sees Jessie's dead body on the roof, the hand holding the pipe is lying at his side. After they leave, the same hand is now on his chest.
Dawson Casting: Averted with Alison Scagliotti as Claudia. Scagliotti is about the same age as Claudia is supposed to be, at most a year or two older (she was 18 for Season 1).
Played straight with Josh Blaylock, who's in his early 20's, playing a fifteen-year-old. Well, more like five hundred and fifteen year old...
Dye Hard: Claudia frequently changes her Skunk Stripe to various unnatural colors. In a DVD commentary it was said that it's a different color every episode. Another commentary revealed that when it's green, it sometimes causes trouble with the green screens.
Fake American: Joanne Kelly (Myka), Saul Rubinek (Artie), Aaron Ashmore (Steve), and Genelle Williams (Leena) are all Canadians playing Americans, as are many guest stars. The show is filmed in the Toronto area.
Fan Nickname: Brent Spiner's character (Brother Adrian, the guardian of the astrolabe) is known in the fandom as Brother Data.
Jo, Zane, and Henry, the first two appearing in the eighth episode and the last in the ninth. SyFy seems to be big on actor sharing.
Which is a little weird, given that the town of Eureka exists in this 'verse'.
Not only exists, but has a full crossover involving all of those characters.
As well as Fargo, twice.
Unless you consider the actual crossover episodes Non-Canon?
"Don't Hate The Player" features Fargo again, referencing the earlier crossovers in the recap. The Artifact (Beatrix Potter's Tea Set) collected there is shown in Season 4's "A New Hope". They're Canon.